The present application, as presently envisioned, relates to mechanical joint packing devices, and more particularly, to a labyrinth sealing device for providing a dynamic seal between a rotating shaft and a bearing housing and, most particularly, to a grease purgeable labyrinth sealing device that is designed to eliminate the failure problems caused by applying excessive grease to the bearings being protected by the labyrinth sealing device.
Before May 1977, rubber lip seals protected the bearings in most industrial process pumps. Only those pumps that were designed for API servicexe2x80x94petroleum refinery duty specificationsxe2x80x94were fitted with labyrinth seals. Those labyrinth seals were designed primarily to keep the lubricant inside the bearing frame. They were ineffective in preventing contaminants from entering the bearing.
A failed lip seal in an HVAC pump prevented occupancy of the Sears Tower in Chicago shortly after it was built. Chilled water was needed to temper the sun load on the south side of the building. Water spray from a leaking mechanical seal entered the bearing housing and the pump shut down. Consequently, the southern windows on the top floors were popping out, making the building uninhabitable. Special labyrinth seals were installed to replace the lip seals and the pump was again in operation.
Because of the lack of reliable bearing protection, pump bearings were short-lived and considered expendable. Contamination by moisture, dust, dirt and the liquid being pumped, even loss of lubricant through the lip seals, was commonplace. Lip seals either grooved the shaft or xe2x80x9ccarbonizedxe2x80x9d at the contact point, allowing free movement of contaminant and lubricant in or out of the bearing housing.
Clearly, a better method of protecting pump bearings were sorely needed, one that would be permanent and effective, and, in effect, xe2x80x9cisolatexe2x80x9d the bearing environment. In 1977, no such device existed in the world. An all-out effort to solve the problem and satisfy the performance gap resulted in the first xe2x80x9cbearing isolators.xe2x80x9d These isolators were compound labyrinth seals, non-contacting, non-wearing and absolute in nature. Field trials proved the effectiveness of the new device, where all other methods of bearing protection had failed.
After quick rejections by nearly every major pump manufacturer in the U.S., the manufacturer of the isolator contacted the pump users in the process industries. After field installation of the new device, it was almost immediately apparent to the users that the enhanced reliability of the pumping equipment would prove to be an economical investment. Pump manufacturers rapidly responded to the customers and installed bearing isolators on new equipment whenever they were specified by users, but only then.
Today, almost every process pump produced in the U.S. is fitted with some sort of labyrinth sealing device. Enlightened pump users are retrofitting most of their repaired pumps and motors. Long-term cost savings and productivity improvements in the process industries are the results.
Shortly after the introduction of the bearing isolator, many competitors entered the niche market. Most offered similar products, but others were made of lightweight PTFE derivatives. Even magnetic face seals were successfully applied as bearing isolators in pumps and gears.
The most common form of rotating equipment in use in the process industries is the three-phase AC electric motor, varying in size for one through 500 horsepower. It is believed that more than 40 million motors are installed in the U.S. alone. Combined, they consume approximately 70 percent of the electrical power generated for industrial use. Motors have been manufactured in essentially their present form for nearly 100 years, without regard to effective bearing protection.
Since the days of Edison and Steinmetz, only rubber flingers or slingers inhibited direct ingress of contamination into the exposed bearing compartment. Therefore, mechanicalxe2x80x94not electricalxe2x80x94failure is the overwhelming cause of motor outage. Users in the process industries recognized the obvious faults in motor design and rated bearing failure as the No. 1 cause of failures in NEMA frame drivers.
The reliability of pumps and motors has vastly improved over the past 20 plus years, due primarily to enhancement of bearing integrity. If a rolling element bearing is kept clean and well lubricated, it will conceivably perform for 150,000 hours (17 years) or more. ANSI pump manufacturers are warranting their pump bearing frames for three years. Motor manufacturers are typically warranting their bearing-protected motors for five years.
Typically, a bearing isolator is a mechanical device that permanently isolates a bearing from its environment. It should be non-contacting and non-wearing and must prevent humidity and moisture from entering the bearing enclosure during start and stop cycles.
Bearing isolators are easy to install, most have an interference fit with the bearing cap or end-bell, so they should be pressed into place with an arbor press, although the user sometimes prefers to tap them with a soft hammer.
Ideally, xe2x80x9cmaintenancexe2x80x9d is the act of keeping equipment in running order. Maintenance is not a xe2x80x9cfix it when it breaks downxe2x80x9d function, as it may have been considered in the past. Reactive maintenance is disruptive of the manufacturing process and therefore an expensive luxury for the manufacturer. Pumps and motors are the most common forms of rotating equipment and require the most attention by the maintenance activity.
Preventive maintenance is also expensive and usually excessive for the job at, hand. Preventive maintenance is usually performed based on elapsed time, whether or not the equipment needs attention. The theory was to prevent catastrophic failures of process equipment by anticipating the weak links in the equipment design and replacing the weak link equipment before the failure thereof.
Predictive maintenance is now the methodology of choice for a majority of process industry professionals. Vibration analysis, thermography usually infrared technology and lubricant condition inspection are commonly used tools that predict a breakdown before it actually occurs.
If a rotating equipment maintenance cycle is less than the ideal design life of the component parts (bearing, mechanical seals or, in the case of electric motors, the electrical insulation), an effort should be made to design maintenance out of the equipment. Instead of spending the entire maintenance effort on condition-based, fixed time, or reactionary maintenance, a good maintenance organization should invest a significant portion of the budget toward cost-avoidance and equipment design enhancements.
Replacing the lip seals in pumps and the flingers and slingers on motor shafts has been proven to increase the mean time between planned maintenance by a factor of two. If the maintenance activity directed to pumps and motors is cut in half each year for three years, such activity will be reduced to 12.5 percent of the current benchmark. A return on investment as high as 400 percent is commonly attainable.
Historically, process pumps have had a useful service life of 2.8 years before being repaired in some way or another. Industrial motors fare much better, averaging 5.7 years until their first repair or replacement. Company personnel usually repair pumps on-site, while motors typically are sent off-site to a repair facility.
To minimize disruption to the maintenance department, pump repairs and bearing isolator upgrades are done in chronological order, according to specific instructional assistance provided by the isolator manufacturer""s field personnel. Motors are sent to the repair facility along with specific instructions and specifications to install bearing isolators on the shaft and fan ends. Manufacturer""s personnel will be on hand, as required, to assist and educate the repair facility employees as to the application and installation of bearing isolators.
Recent reliability enhancements to pumps and motors have had a significant impact on the productivity of maintaining rotating equipment in the process industries. Over their useful lives, pumps and motors consume much more maintenance and power costs than their original price tags. Users now analyze and value total life cycle costs when evaluating manufacturer""s offerings. An initial modest investment in superior bearing protection in pumps and motors will pay dividends for years to come.
The bearing isolator is a design of compound labyrinth seal specially adapted to protect bearings in rotating equipment. It has only two major partsxe2x80x94a rotor and a statorxe2x80x94but is assembled as a single unit, locked together by an internal vapor-blocking O-ring. The unit is press fitted into the bearing housing, using the same cavity that would be used for a lip seal or flinger. In addition to the mechanical lock-up on O-rings gasket seals the stator to the housing.
The rotor fits over the shaft and is driven by one or more O-rings. The drive ring(s) act as a seal against the shaft. The rotor and stator do not touch, so they do not wear out. Before contaminants, such as dirt or water, can get into the bearing housing, they must pass through a complex labyrinth pattern involving grooves, expansion chambers and direction changes. Contaminants are collected and expelled back into the environment through an expulsion port in the stator. Similarly, lubricant is drained back into the bearing housing by means of collection grooves and gravity drain.
When the equipment is at rest, the internal O-ring engages both the rotor and stator and thus hermetically seals the bearing housing from humidity. Upon start-up, the O-ring turns with the rotor and centrifugal force circumferentially stretches and expands it so it no longer touches the stator and hence, does not wear.
Labyrinth type rotary shaft seals are well known in the art. Typically, these devices include two concentric ring structures, which define a rotor and a stator. The rotor is sealing engaged with a rotating shaft, and the stator is sealingly engaged with a bearing housing. Specifically contoured pathways or grooves are formed in the interior surfaces of the seal rings to create a maze or labyrinth extending between the exterior of the bearing housing to the interior of the bearing housing. The labyrinth pathway serves as a hydrodynamic barrier to maintain fluid lubricants within the bearing housing and prevent contaminants from entering the bearing housing. The more elaborate the pathway, the less chance there is that contaminating materials will pass through the structure and into the bearing housing. One way of making a more elaborate pathway is to increase the amount of surface area that must be traversed by contaminating materials, i.e., increase the length of the pathway.
In general, the extent of the surface area of the labyrinth pathway will be limited by the degree of mechanical interlock between the two components of the device upon assembly. If the interlocking contact area between the components is relatively small, there will be less surface area to form a labyrinth pathway therebetween. Conversely, if the interlocking contact area between the two components is relatively large, there will be a greater surface area to form a more elaborate labyrinth pathway between the two components.
An example of a prior art labyrinth sealing device in which there is a low degree of mechanical interlock between the rotor and the stator is disclosed in U.S. Pat. No. 4,466,620 to Orlowski. In the Orlowski device, the rotor is provided with an axially extending annular flange for engaging a complementary axially extending annular recess formed in the stator. An example of a prior art labyrinth sealing device in which there is a high degree of mechanical interlock between the rotor and the stator is disclosed in U.S. Pat. Nos. 5,316,317 and 5,431,414 to Fedorovich et al. This is mechanical interlock is achieved during assembly by initially heating the connective portion of the stator to expand the diameter thereof. The connective portion of the rotor is then positioned radially inside of the connective portion of the stator. The stator is then permitted to cool to effect the interlock between the two components.
Although the Fedorovich et al. device provides an elaborate labyrinth pathway to prevent contaminants from passing through the structure, its method of assembly is both time consuming and inefficient. Accordingly, until recently a need existed in the art to provide a labyrinth type rotary shaft seal in which there is a high degree of mechanical interlock between the component parts thereof that can be assembled quickly and efficiently.
U.S. Pat. Nos. 6,015,193 and 5,908,195 solved a considerable number of the mechanical interlock and assembly issues. However, no solution has been proposed to eliminate the problem caused by the application of excessive grease to bearings in the bearing housing and the resultant dislodgment of the labyrinth sealing devices protecting the bearings in the bearing housing. Thus, there is a need in the art to provide a labyrinth type shaft seal that significantly reduces, if not totally eliminates, that dislodgment of the labyrinth sealing devices when excess grease has been applied to the bearing housing.
Such labyrinth type rotary shaft seals should provide a means for allowing the excess grease to flow through the stator of the labyrinth type rotary seals and be directed away from the labyrinth type seals without the labyrinth type rotary seals being dislodged from their protective position relative to the bearing housing or the labyrinth becoming clogged with any of the excess grease. Such labyrinth type rotary shaft seals should provide for increased resistance to dislodgment from the protective position relative to the bearing housing when pressure, such as excess grease, from the bearing housing side of the seal, which would tend to move the seal away from the bearing housing, is increased. Such labyrinth type rotary shaft seals should provide means for grease to be routed from the bearing housing, through the stator of the labyrinth type rotary seals while the labyrinth type rotary seal remains in the proper position relative to the bearing housing in order to protect the bearings from contamination. Such labyrinth type rotary shaft seals should provide means for reducing the contact area between the stator and the rotor should the stator and the rotor be forced together in order to extent the useful life of labyrinth type rotary seals.
The subject invention is directed to grease purgeable dynamic labyrinth sealing devices for placement between a rotating shaft and a bearing housing. The device includes a stator for sealingly engaging the bearing housing and a rotor for sealing engaging the rotating shaft. An elaborate labyrinth pathway is defined between the stator and rotor for preventing contaminants from passing through the device. The stator has an annular engagement flange on a radially inner portion thereof and the rotor has an annular engagement flange on a radially outer portion thereof. The stator annular engagement flange and the rotor annular engagement flange have coacting means for mechanically interlocking the stator and the rotor. Once interlocked, the annular engagement flanges form part of the labyrinth pathway.
Preferably, the coacting means includes an outer radial engagement notch formed in the stator engagement flange and an inner radial engagement notch formed in the rotor engagement flange. The outer radial engagement notch and the inner radial engagement notch include complementary angled engagement surfaces. The stator engagement flange and the rotor engagement flange each have opposed leading and trailing axial surfaces, and the complementary angled surfaces of the radial engagement notches are dimensioned and configured to facilitate progressive opposed lateral deflection of the engagement flanges and effectuate juxtaposition of the leading axial surface of the rotor engagement flange and the trailing axial surface of the stator engagement flange.
In accordance with the subject application, at least one annular recess is formed in a radially outer portion of the stator for supporting an elastomeric O-ring between the stator and the bearing housing. Similarly, at least one annular recess is formed in a radially inner portion of the rotor for supporting an elastomeric O-ring between the rotor and the rotating shaft. In addition, at least one aperture having a counter sink, presently preferred, about a forty-five degree (45xc2x0) counter sink, is formed in the portion of the stator that is most proximate to the bearing housing in a location such that any material that enters the aperture is directed down from the stator via a drainage or expulsion port. In its presently preferred embodiment, at least one aperture and presently preferably, seven (7) apertures are formed the stator such that each aperture is operatively connected to the expulsion port.
At least one annular groove is formed in the radially outer portion of the rotor, in a location spaced from the engagement flange thereof, for capturing contaminants drawn into the grease purgeable dynamic labyrinth sealing device from outside the bearing housing. A radial exhaust slot or expulsion port is preferably formed in the stator to facilitate the expulsion of captured contaminants from the sealing device. An annular sealing lip projects from a leading edge of the radially outer portion of the stator for sealingly engaging a leading edge of the radially outer portion of the rotor, providing an additional barrier to contaminants.
In accordance with a preferred embodiment of the subject application, means, such as, for example, a plurality of apertures are operatively formed in the stator for allowing excess grease applied to the bearing housing to move through the stator and out of the stator such that the grease purgeable dynamic labyrinth sealing device maintains proper position relative to the bearing housing and is rotatable with the""shaft.
In accordance with another preferred embodiment of the subject application, means, operatively formed on the rotor for reducing the size of the contacting surface area between the stator and the rotor such as, for example, an annular ring or protrusion formed on the surface of the rotor which contacts the stator or vice versa.
In accordance with yet another preferred embodiment of the subject application, means, operatively formed on the stator, are provided for increasing the resistance of the stator to move away from the bearing housing when excess grease exits the bearing housing between the bearing housing and the stator, such as, for example, more shallow portions of the O-ring grooves that allow the O-rings to compress when the stator is moved away from the bearing housing.
An object of the present application is to provide a grease purgeable dynamic labyrinth sealing device for preventing the application of excess grease to the bearing housing from dislodging a grease purgeable dynamic labyrinth sealing device.
Another object of the present application is to provide s a grease purgeable dynamic labyrinth sealing device for routing excess grease from the bearing housing thorough the stator and outside a grease purgeable dynamic labyrinth sealing device.
A further object of the present application is to provide a grease purgeable dynamic labyrinth sealing device for resisting axial displacement away from the bearing housing when excess grease applies pressure to the bearing housing and the grease moves past the bearing housing toward the stator of the grease purgeable dynamic labyrinth sealing device.
Yet a further object of the present application is to provide a grease purgeable dynamic labyrinth sealing device for increasing the contact pressure between the stator O-rings and the bearing housing when pressure is applied to a grease purgeable dynamic labyrinth sealing device from the direction of the bearing housing.
Yet another object of the present application is to provide a grease purgeable dynamic labyrinth sealing device for maintaining the position of a labyrinth seal relative to a bearing housing when excess grease is applied to the bearings in the bearing housing.
In accordance with these and further objects, one aspect of the present application includes a dynamic sealing device for placement between a rotating shaft and a bearing housing comprising: a stator having an annular engagement flange on a radially inner portion thereof and fluid passage means, operatively formed in the portion of the stator most proximate to the bearing housing, for allowing fluid to move from the bearing housing through the stator and out of the stator; and a rotor having an annular engagement flange on a radially outer portion thereof, the stator and the rotor being operatively connected.
Another aspect of the present application includes a dynamic sealing device for placement between a rotating shaft and a bearing housing comprising: a stator having an annular engagement flange on a radially inner portion thereof and fluid passage means, operatively formed in the portion of the stator most proximate to the bearing housing, for allowing fluid to move from the bearing housing through the stator and out of the stator; a rotor having an annular engagement flange on a radially outer portion thereof, the stator and the rotor being operatively connected; and grooves, operatively positioned on the stator, the grooves including means for increasing the contact pressure between O-rings operatively positioned in the grooves for interacting with the bearing housing when pressure is applied to the dynamic labyrinth sealing device from the direction of the bearing housing.
Still another aspect of the present application includes a dynamic sealing device for placement between a rotating shaft and a bearing housing comprising: a stator having an annular engagement flange on a radially inner portion thereof and fluid passage means operatively formed in the portion of the stator most proximate to the bearing housing, for allowing fluid to move from the bearing housing through the stator and out of the stator; and a rotor having an annular engagement flange on a radially outer portion thereof and an annular ring operatively formed on the portion thereof that contacts the stator when the rotor and the stator are forced into contact when the rotor rotates, the stator and the rotor being operatively connected.
Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.